The piezoresistor sensor has been used in many applications to measure pressure or force. The assignee herein, namely Kulite Semiconductor Products, Inc. holds over 150 patents on pressure sensor design and the technology is well known. In regard to such pursuits, it has been determined that there is a need for a compact and economical absolute and gage pressure transducer. Such transducers can be utilized in the automobile industry, as well as many other industries. As one can ascertain, these devices have to be reliable and extremely economical. Furthermore, the devices have to be compact in order to take up less room and consume less power. As one can ascertain in the automotive industry, pressure transducers are employed to measure the pressure of various engine fluids and to measure the pressure at the manifold and so on. The devices have to be extremely reliable. As one can understand, differential pressure measurements can be accomplished by a differential transducer which provides an output which is the difference between two input pressures. In the case of a gage sensor, one of these pressures is atmospheric pressure and the other pressure is the pressure being monitored. Essentially a gage transducer provides an output which is the difference between atmospheric pressure and the monitored pressure. In the case of the absolute pressure transducer, the output is indicative of monitored pressure.
As one can ascertain from the prior art, such devices exist while there can be many problems. One typical problem, in the case of an absolute transducer, is that it is difficult using standard integrated circuit chip fabrication and packaging techniques to form a reference pressure on the circuit side of the sensing diaphragm. Other configurations are deficient in that there has to be extreme care in positioning the piezoresistive sensing device in the package so that it is properly aligned in order to receive the common input pressures. This has been a difficult job and requires an experienced assembly technician to align the integrated circuit chip within the housing so that the optimum pressures can be applied to the chip. Other problems exist in regard to the difficulty of providing a compact device which will also be rugged and reliable. As one can ascertain, the smaller one makes the device, the more difficult it is to operate the same and to construct the same in a reliable manner. In any event, the prior art is replete with the number of patents which describe absolute and gage sensors.
For example, reference is made to U.S. Pat. No. 4,222,277 issued on Sep. 16, 1980 to A. D. Kurtz, et al. and entitled Media Compatible Pressure Transducer. This patent is assigned to Kulite Semiconductor Products, Inc., the assignee herein. As one can ascertain, that patent discloses an absolute and gage pressure transducer which are contained on a single wafer, where the wafer contains a gage sensing configuration on one portion and an absolute sensor configuration on the other portion. In any event, the device depicted responds to and produces an output proportional to both absolute and to gage pressure.
Reference is also made to U.S. Pat. No. 5,955,771 entitled Sensors for Use in High Vibrational Applications and Methods for Fabricating Same issued on Sep. 21, 1999 to A. D. Kurtz, et al. and assigned to Kulite Semiconductor Products, Inc., the assignee herein. That patent is pertinent as it shows a technique for fabricating semiconductor devices which are designated as leadless devices and which devices can be utilized in the invention to be described.
In regard to absolute differential pressure devices reference is made to U.S. Pat. No. 6,612,179 entitled Method and Apparatus for the Determination of Absolute Pressure and Differential Pressure Therefrom. That patent was issued on Sep. 2, 2003 to A. D. Kurtz, the inventor herein and assigned to Kulite Semiconductor Products, Inc. The patent describes a combination of absolute and differential pressure sensing devices or transducers, where each transducer includes a plurality of a half bridge structure and a device for selectively coupling one half bridge structure of one absolute pressure transducer to at least one resistor. As one can see, the patent describes in detail the device employed as well as showing the wafer and glass supporting members. As well can be explained and seen in FIGS. 7A and 7B the device has similar attributes to the device to be described herein.
Also reference is made to U.S. Pat. No. 7,057,247 issued on Jun. 6, 2006 to A. D. Kurtz, et al. and assigned to Kulite Semiconductor Products, Inc. and entitled Combined Absolute Differential Transducer. This patent discloses a combined absolute and differential pressure transducer which consists of two sensors made from the same wafer of silicon and selected to be adjacent to each other on the wafer. As one can ascertain from reviewing the patent, which has nineteen Figures, the device depicted therein provides a relatively inexpensive structure which is capable of measuring both absolute and differential pressures.
References also made to U.S. Pat. No. 7,107,853 entitled Pressure Transducer for Measuring Low Dynamic Pressures in the Presence of High Static Pressures issued on Sep. 19, 2006 to A. D. Kurtz, the inventor herein, and assigned to Kulite Semiconductor Products, Inc., the assignee herein. In that patent a sensor is described which consists of a leadless high sensitivity differential chip which responds to both static and dynamic pressure. Located on the transducer are two sensors. One sensor has a thicker diaphragm and responds to both static and dynamic pressure to produce an output indicative of essentially static pressure. The other sensor has a thinner diaphragm as one side or surface responds to both static and dynamic pressure. The other side of the differential sensor has a reference tube coupled to the bottom of the diaphragm. The tube only allows static pressure to be applied to the underside of the diaphragm. In any event, as one can see from the structure a single chip is employed. In any event, in view of the above, as one can ascertain, there are many patents which exist in the prior art which show the absolute and differential gage pressure transducers employing a single chip having two sensor circuits located on the chip and employing various header designs. As indicated above, it is a problem in regard to such prior art devices to accurately fabricate the device so that the chip is in proper alignment with respect to the pressure ports and that the device is compact and capable of being quickly and reliably assembled. It is an object of the present invention to provide a compact absolute and gage pressure transducer having these features.